index_US.html, index_UK.html, index_FR.html, index_CN.html, index_IN.html, index_RU.html , etc...
Lookup the IP address of the visitor to get the respective country code (use an appropriate api or database that maps IP address to country, example below uses API from ipapi.co that I've been a consultant for ). The country name is returned in plain text as 2 digit ISO code e.g. 'US' for USA, 'UK' for UK and so on.
redirect to specific page